Vacuum pumps are well known and widely used in a variety of industrial environments. In the environment of the apparatus of the present invention, vacuum pumps are extensively used to remove reaction gases from process equipment. As an incident to the removal of such gases, certain airborn particulates may also be removed. For instance, in the manufacture of integrated circuits, a number of etching steps are required during which various conductive or nonconductive layers are applied with a stencil, or mask, to a silicon wafer, with the surrounding material being thereafter removed or etched therefrom. Because of the extreme miniaturization of the electrical components in an integrated circuit chip, any particulate contamination of a size greater than about 0.3-0.5 micron can adversely affect the proper perfromance of the finished product. Therefore, vacuums are applied to the hoods, or enclosed spaces, within which the fabrication of such circuits is effected. It is of critical importance that all airborne contamination whether in the form of a gas or particule, be removed from such enclosures.
While the vacuum pumps of the prior art function adequately in many environments, it is not uncommon that the pumps fail prematurely due to ineffective filtration of the recirculating vacuum oil. Further, the addition of make-up oil or a total recharge of oil after an oil change, was difficult to effect. Therefore, it is an object of the present invention to provide an apparatus which will effectively filter recirculating vacuum oil and permit its easy addition to the system.